Heretofore, as shown in the following literatures, there have been reported by Nakamura, Iwanaga, Niwa, et al. polypeptides (Tachyplesin and Polyphemusin) exhibiting an affinity to endotoxins and being derived from horseshoe crabs and their pharmacological properties.
(i) J. Biol. Chem., 263, 16709-16713 (1988)
(ii) Published Searched Application 500194/1990
(iii) Chem. Pharm. Bull., 37, 2661-2664 (1989)
(iv) Japanese Laid-Open Patent Publication No. 53799/1990
(v) Japanese Laid-Open Patent Publication No. 152987/1990
(vi) Japanese Laid-Open Patent Publication No. 167230/1990
(vii) J. Blochem., 106, 663-668 (1989)
(viii) Taisha (Metabolism), 26, 301-311 (1989)
As for polypeptides having an affinity to endotoxins isolated from horseshoe crabs (the genus Tachypleus, the genus Lumulus and the genus Carcinoscorpius), 5 structural analogs exist, to the best of researcher's knowledge, and each of them is a polypeptide having a cyclic structure comprising 17 or 18 natural amino acids. Further, these polypeptides mutually exhibit extremely analogous properties, and such a polypeptide is very interesting as one of key substances whereby horseshoe crabs have been able to be adapted to changes of their external environment and preserve their species from ancient times to the present time as a living fossil.
On the other hand, with respect to maintenance of the existence of human beings who have highly differentiated, drugs are being desired which are expected to have a prophylactic or therapeutic effect on an acquired immune deficiency syndrome (AIDS) caused by infection with a human immunodeficiency virus.
The present inventors paid their attention to the above endotoxin-affinitive polypeptides conjectured to have relation to the strong preservability of species on horseshoe crabs, and made a study of a correlation between structural changes on these substances and the anti-human immunodeficiency virus (HIV) activity. As a result, they found novel polypeptides basically different from the common structure of the known endotoxin-affinitive polypeptides of horseshoe crabs, and, to their surprise, it was ascertained that these novel polypeptides have an excellent effect that their anti-HIV activity values are 10 times or more as large as that of a known endotoxin-affinitive polypeptide.